This invention relates to drilling horizontal bore holes, and, more particularly, to stabilizing horizontal borehole walls.
Many uses arise for horizontal bore holes, particularly in the field of environmental remediation where a geologic structure must be followed for contaminant monitoring and removal. There are several considerations relative to drilling horizontal boreholes. A first consideration is forming the borehole itself, i.e., drilling the passage through the earth. A second consideration is the support of the bore hole walls. Next, as the hole is drilled, the bore hole cuttings must be removed from the borehole. The final consideration is the installation of a casing and, optionally, a well screen within the borehole.
In conventional drilling, a drilling mud is circulated around a drill bit in order to flush the cuttings from the drill from the hole. The drilling mud is commonly formed of a composition that will form a mud cake on the borehole wall and support the borehole walls against collapse. Drilling mud exerts pressure against the hole wall, which then supports the wall. If the drilling mud cannot support the hole wall, the walls will collapse and greatly impede emplacement of the casing and any well screen provided with the casing.
In drilling horizontal holes for remediation of contaminated geologic formations, however, the drilling mud acts to plug the pore space of the formation. The plugging effect of the drilling mud drastically reduces the permeability of the geologic formation to fluid flow into or out of the hole. The plugging effect is especially pronounced in loosely consolidated sands and gravel that are often the preferred flow paths of contaminates in the geologic structure.
It will also be-appreciated that the drilling muds that effectively support the borehole walls also circulate very slowly in large diameter bore holes. This slow circulation velocity reduces the effectiveness of the drilling mud to remove the drill cuttings from the borehole.
Patent application Ser. No. 08/769,656, now U.S. Pat. No. 5,803,666, "Horizontal Drilling Method and Apparatus," filed Dec. 19, 1996, incorporated herein by reference, describes a liner system that supports a bore hole and reduces friction during casing installation in a bore hole. The liner system is designed to be removed from about the casing after casing installation so that the casing and any screens thereon can directly contact the bore hole walls for communication with the surrounding structure. But, in many instances, there is no need to communicate with the geologic structure and no need for the complications associated with liner removal from about an installed casing.
Accordingly, it is an object of the present invention to provide an alternate means for supporting the wall of a borehole during horizontal drilling.
It is another object of the present invention to avoid the buildup of mud cake on the bore hole wall and improve the removal of cuttings out of the borehole.
Yet another object of the present invention is to provide a simple liner system for use in casing installation in a borehole.
One other object of the present invention is to reduce the forces on the hole casing during emplacement in the borehole.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.